The present invention is directed to methods and apparatus for performing interpolated timing recovery (ITR), and more particularly to using an estimated frequency and phase of an asynchronously sampled sector to perform timing recovery.
In magnetic storage systems, a read head reads back data stored on a disk platter by analyzing the magnetic field generated by a particular storage region (e.g., a sector or data sector). The read head generates an analog signal representing the storage portions as the read head passes over various disk sectors. The analog signal is sampled and processed in the digital domain, by for example, using a Baud-rate sampling process. It is desirable to have the sampling rate be the same as the binary data rate for optimal data sampling.
Additionally, it is desirable to select an optimal sampling phase out of all the possibilities between 0 and 1 clock cycles for use in processing the data. Timing recovery is performed to determine the optimal sampling rate (i.e., sampling frequency) and the optimal sampling phase.
Typically, timing recovery in magnetic recording systems is decision aided. In particular, a Viterbi detector provides information (e.g., bit decisions) to a phase-loop and/or a frequency-loop in a closed-loop continuous manner as signals are read back from the disk. However, the Viterbi detector has a high raw bit-error-rate (BER) for low signal-to-noise ratio (SNR) signals casing instability in the frequency and/or phase loops.
Compensation for this instability is performed by maintaining a minimum bandwidth at the timing loop. However, a frequency offset may still be present which can be compensated by avoiding a bandwidth that is too small. Traditional systems must operate under these competing demands to provide optimal timing recovery.
Accordingly, it is desirable to provide enhanced systems and methods for performing timing recovery under optimal bandwidth conditions.